Weekly repeat sets 'From' time to 00:00

Drupal 6.22, PHP 5.3.6.

Weekly repeats sets second and subsequent records to start from 00:00. Timezone handling set to 'Site's timezone'.

Repeats every week until Fri Aug 19 2011 .
20 June, 2011 - 14:38 - 15:43 (ok)
27 June, 2011 - 00:00 - 01:05 (wrong)
4 July, 2011 - 00:00 - 01:05 (wrong)
...
15 August, 2011 - 00:00 - 01:05 (wrong)

First record is OK and other begin from 00:00. That is wrong.

Database check shows the following:

field_datetime_value field_datetime_value2 field_datetime_timezone
2011-06-20T10:38:00 2011-06-20T11:43:00 RRULE:FREQ=WEEKLY;INTERVAL=1;UNTIL=20110819T155959...
2011-06-26T20:00:00 2011-06-26T21:05:00 RRULE:FREQ=WEEKLY;INTERVAL=1;UNTIL=20110819T155959...
2011-07-03T20:00:00 2011-07-03T21:05:00 RRULE:FREQ=WEEKLY;INTERVAL=1;UNTIL=20110819T155959...
2011-07-10T20:00:00 2011-07-10T21:05:00 RRULE:FREQ=WEEKLY;INTERVAL=1;UNTIL=20110819T155959...
... and so on.

Monthly and yearly repeat works as expected.

Actually I don't know what to check to get it completely clear. Please, help.